1. Field of the Invention
The present invention relates to wireless communication systems.
2. Description of the Related Art
Wireless communications system employ a number of geographically distributed cellular communication sites or base stations. FIG. 1 illustrates a representative wireless communications system 20 showing a base station 22 that supports transmission and reception of communication signals to and from various stationary or movable devices serving as mobile stations 23, such as a wireless phone 24, a personal digital assistant 26, or a computer 28. The base station 22 includes a system controller 30 that includes known radio equipment and signal processing equipment that generate and process data and communication signals in a wireless network.
In one embodiment, each base station 22 may transmit and receive signals to and from the mobile devices via an antenna 32 mounted on a tower 38. The controller 30 may include the necessary electronics and software for deciphering and managing signals received by the antenna 32 and for generating or transmitting the signals necessary to achieve the communications desired at the mobile stations 23 within the network. Note that the devices serving as mobile stations 23 may actually be stationary or fixed.
Each base station handles communications over a particular region commonly referred to as a cell/sector. The overall coverage area for a wireless communications system is defined by the union of cells for the deployed base stations. Here, the coverage areas for adjacent or nearby cell sites may overlap one another to ensure, where possible, contagions communications coverage within the outer boundaries of the system.
When active, a mobile device receives signals from at least one base station 22 over a forward link or downlink and transmits signals to at least one base station over a reverse link or uplink. Several approaches have been developed for defining links or channels in a cellular communication system, including, for example, TDMA (time-division multiple access), and CDMA (code-division multiple access).
In TDMA communication systems, the radio spectrum is divided into time slots. Each time slot allows only one user to transmit and/or receive. Thusly, TDMA requires precise timing between the transmitter and receiver so that each user may transmit their information during their allocated time.
In CDMA communications systems, different wireless channels are distinguished by different channelization codes or sequences. These district channelization codes are used to encode different information streams, which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream from a received signal using the appropriate code or sequence to decode the received signal.
With the explosion of the Internet and the increasing demand for data, resource management has become a growing issue in cellular communication systems. Next generation wireless communication systems, such as those employing an Enhanced Uplink Dedicated Channel (“EUDC”), are expected to provide high rate packet data services in support of Internet access and multimedia communication. Even though the EUDC focuses on providing high-speed data on an uplink channel, the EUDC still requires a supporting downlink channel to carry control information (e.g., power level, channelization codes, etc.) from the base station 22 to the mobile station so that the mobile station will know how to transmit data on the uplink.
While it may be possible to construct new shared control channels on the downlink to handle the EUDC control information, creating new shared channels may require large downlink capacities. New shared channels require high amounts of transmission power to meet transmission performance requirements, but high transmission power also generates downlink inter-cell and intra-cell interference due to non-orthogonality among adjacent cells and a multipath effect. Further, there may be mobile stations that cannot support EUDC control information over a new channel without additional hardware, making implementation of high-speed transmissions less convenient.
There is a desire for a system and method that allows EUDC control information to be sent on a downlink channel to mobile stations while minimizing interference.
There is also a desire for a system and method that enables mobile stations to support EUDC control information without requiring extensive hardware modifications.